Blow-molding apparatus of more-or-less standardized construction has long been used to produce bottles from plastic resins. Halves of a mold are mounted opposite each other on platens; the platens are driven toward each other by a toggle mechanism to close the mold and to hold the mold closed during a brief blow-molding interval. Reverse operation of the mechanism opens the mold, allowing removal of the blowmolded bottle. While the mold is open, a roughly cylindrical parison of heat-softened plastic resin is moved over a blow pin and extends across the space between the mold halves from the neck-forming portions of the mold to a position beyond the portions of the mold that form the bottom of the bottle. The blow pin is positioned between the mold halves.
When the mold closes, the free end of the parison is sealed shut by the bottom-forming portions of the mold halves. At the same time, half-circle sealing rims in the neck-forming portions of the mold seal the parison around a seal-forming ring of the body of a blow pin. A high-pressure burst of air then enters the parison via the blow pin, causing the parison to expand against the surfaces of the mold, thus shaping the bottle.
The neck portions of the mold halves include half-circle shearing edges coaxial with the half-circle sealing rims. As soon as the bottle has been shaped by the burst of air inflating the parison against the surfaces of the mold cavity, the blow pin is shifted axially in a short stroke such that a shearing ring of the body of the blow pin cooperates with the shearing edges at the neck-forming portion of the mold to sever the neck of the bottle from scrap that is produced in the operation.
The half-circle sealing rims and the half-circle shearing rings become worn and must be replaced periodically. They are removably secured to the neck-forming portions of the mold halves by what may be called a mounting base or, briefly, a "base". In the standardized blow-molding apparatus, the base is circular and it is called a "base ring". U.S. Pat. No. 4,032,278, issued Jun. 28, 1977, shows a now-standard assembly of a base ring, sealing elements and shearing elements designed for easy replacement when they become worn.